中国东部大陆边缘中生代晚期增生过程的数值模拟:以那丹哈达为例

Numerical simulation of Late Mesozoic accretion process along the continental margin of East China:A case study of the Nadanhada Terrane

许多现存造山带中均发现了洋岛玄武岩(OIB)和地幔柱型蛇绿岩记录,因此洋底高原增生是大陆生长的重要方式,但目前对控制洋底高原增生过程的机制仍不清楚。采用热-机械-岩石学模型数值模拟研究洋底高原的陆缘增生过程,结果显示洋底高原向大陆边缘增生具有3个控制因素:(1)减薄的大陆边缘;(2)海洋岩石圈中的“薄弱”层;(3)年轻的洋底高原。模拟结果与中国东北地区那丹哈达地体的野外构造解析结果和地球化学特征结合,揭示了洋底高原和东北亚大陆边缘的强烈挤压引起俯冲带的应变集中,产生与阿尔卑斯型褶皱相关的高角度逆冲断层和背冲断层,并伴随低级变质作用的构造折返过程。

Accretion of oceanic plateau is an important process of continental growth,and is exemplified by the presence of oceanic island basalts (OIB) and plume-type ophiolites in many modern orogens.Oceanic plateau can also subduct along convergent margins,as revealed by seismic tomography.The mechanism controlling accretion or subduction of oceanic plateau remain unclear.In this paper,we investigate the accretion of oceanic plateaus at continental margins using a thermo-mechanical-petrological model of an ocean-continent convergent zone.The results of the models show three major factors for the accretion of the oceanic plateaus onto the continental margin:(1) thinned continental margin for the overriding plate,(2)“weak” layers in oceanic lithosphere and (3) young oceanic plateau.The results of the model are further compared with the field structural analysis and geochemical characteristics of the Nadanhada Terrane in Northeast China.It is revealed that the intense compression of the seamount and the continental margin of Northeast Asia results in strain concentration in the subduction zone,forming high-angle thrust faults and back thrusts associated with the Alpine-type folds,and structural exhumation of low-metamorphic rocks through thrust faults.